Make the crust: In a food processor, combine the flour, salt, and butter. Process at low speed for 10 seconds, until the mixture resembles coarse meal. Add the egg and mix again for a few seconds, until the dough comes together into a ball. If the dough is still a little dry, add a little ice-cold water, 1 teaspoon [5 ml] at a time, and process again in short pulses until the dough comes together. Turn out on a lightly floured work surface and gather into a slightly flattened ball without kneading. Wrap tightly in plastic and refrigerate for 30 minutes or up to a day. Let stand at room temperature before using, just long enough that the dough can be rolled out without cracking, about 10 minutes.

Preheat the oven to 350ºF [175ºC]. Grease a 10-inch ceramic tart pan with 1 teaspoon [5 ml] olive oil. Working on a lightly floured surface, roll out the dough in a 12-inch circle. Transfer the dough into the pan, prick the bottom all over with a fork, and press on the sides with your fingers so the dough will adhere. Bake for 7 minutes, until lightly golden. Remove from the oven (leave the heat on) and set aside.

Make the filling: While the crust is baking, heat 2 tbsp [30 ml] olive oil in a large pan over medium-high heat and cook the onion until translucent (about 3-4 minutes). Add the Swiss chard and cook until wilted. Remove from the pan and set aside to cool. In the same pan, quickly sauté the slices of prosciutto to get them nice and crispy. Remove from the pan.

In a large bowl, whisk together the eggs, milk, salt, pepper and nutmeg. Layer the onion and Swiss chard at the bottom of the crust and slowly pour the egg mixture over it. Top with slices of prosciutto and crumbled goat cheese. Bake the tart for 30 minutes or until the tart is golden brown and the custard is cooked. Sprinkle with freshly chopped thyme and serve.